Traditionally, designs for a variety of applications used dedicated digital signal processing (DSP) chips or application-specific standard products (ASSPs) to process digital information using signal processing algorithms. Filtering, video processing, and audio processing were just a few of the many applications using digital signal processors.

Now, with performance and capacity improvements to FPGAs, as well as the improved efficiency of common arithmetic operations usually found in most DSP applications, FPGAs doing DSP functions are becoming more common. In many cases both processors and FPGAs are used in the same application, in a co-processing architecture where the FPGA does pre- or postprocessing to accelerate processing speed.

DSP applications are usually difficult to verify via software simulation because of the enormous number of cycles required to process a meaningful data stream; thus, it is usually better to use a hardware development platform to prove out the key parts of a new design. The new DSP design kits from Avnet provide a powerful, flexible, and expandable platform to validate even the most complex signal processing designs that use both FPGAs and DSPs.

Avnet DSP Design Kits
Avnet Design Services has created a variety of DSP-oriented design kits for use with Xilinx® FPGAs and Texas Instruments™ (TI) DSPs. The Spartan-3™-based design kit is optimized for simple video applications, while the Spartan-IIE™-based kit is targeted at audio applications.

The Virtex-II Pro™ kit features an adaptor card that interfaces to TI DSPs and is meant for co-processing applications where the FPGA is offloading significant processing and control functions from the digital signal processor. Each of these design kits also includes a variety of software tools from Xilinx, The MathWorks, and TI. Let’s describe these kit components in more detail.

DSP Co-Processing Design Kit
The DSP Co-Processing Design Kit features a Virtex-II Pro evaluation board, shown in Figure 1. This board contains a Xilinx XC2VP7-FF896 FPGA, eight SMA connectors for high-speed I/O, on-board DDR SDRAM (64 MB), up to 30 LVDS pairs, user I/O switches/LEDs, and several expansion connectors.

Two of the expansion connectors are compatible with the TI adaptor daughtercard (shown in Figure 2) and can connect to TI DSPs. Example designs show how to interface directly with the TI processor using the Xilinx EDK toolset and a direct memory interface approach.

A co-processing-oriented application can use the hardware platform, demonstration designs, and included tools as a great starting point for prototype design and algorithm development. DSP applications are often very difficult to simulate in software, so the ability to quickly create a hardware/firmware/software platform can cut development time significantly. Using the co-simulation tools available in the Xilinx tool suite through The MathWorks Simulink™ and the target hardware is one technique that can dramatically reduce design time.

Additionally, deciding what portions of the algorithm to process in the DSP and which portion to process in the FPGA can often best be done with a trial-and-error approach, using real hardware to quickly evaluate the performance of various options. For example, the number of data streams that can be pre-processed by an FPGA before post-processing by a DSP will depend on many factors – the “burstiness” of the incoming data, the “accept” response rate of the DSP, the size of the buffer memories, the bandwidth of the system bus, and the amount of pre-processing allocated to the FPGA. These are all difficult decisions to make without doing some detailed hardware prototype-based analysis.

The DSP Co-Processing Design Kit also includes the following software tools, as evaluation versions, from the Xilinx XtremeDSP™ Software Evaluation CD Kit: Xilinx ISE 6.2 Foundation™, ChipScope™ Pro, Xilinx System Generator for ISE 6.2, The MathWorks MATLAB™, and Simulink.

Video DSP Design Kit
The Video DSP Design Kit targets simple DSP-oriented video applications in the industrial security, consumer, and automotive markets. Algorithms for video processing like image recognition, video encode, video decode, and video image enhancement are all very difficult to prototype and evaluate without actual hardware on which to run the software or firmware. Using a DSP Design Kit, with some simple video capabilities, can make it much easier and quicker to prototype and evaluate various algorithms and architecture alternatives.

The Video DSP Design Kit features a Xilinx Spartan-3 XC3S400-FG456 or XC3S1500-FG456 FPGA, Platform Flash configuration PROM, expansion connectors, 32-bit PCI edge connector, 10/100 Ethernet port, video DAC, RS-232 console, PS2 keyboard and mouse ports, simple analog I/O, 1 MB SRAM, 256 Kb serial EEPROM, and a variety of user switches and LEDs.

The kit also includes example designs and user documentation to make it easy to get started on a new video DSP design. Several Xilinx application notes and reference designs (some using Xilinx IP cores available from the DSP System Generator tool) are available online to provide even more of a head start (see Table 1). The Xilinx DSP Central website (www.xilinx.com/products/design_resources/dsp_central/grouping/index.htm) has a complete list.

Table 1 – DSP demos in Xilinx System Generator

Digital Communications	16.QAM demodulator for software-defined radio A QAM system with packet framing and FEC for telemetry channels Concatenated FEC codec for DVB standard Costas loop carrier recovery Digital down converter for GSM applications
Signal Processing	A/D and delta-sigma D/A conversion FFT/IFFT in streaming mode LMS-based adaptive equalization Custom FIR filter reference library Polyphase 1:8 MAC-based FIR using SRL16ES IIR filtering: multi-channel, folded implementation IIR filtering: 2nd-order Direct Form I implementation
Image Processing	2D DWT filter 2D filtering using a 5 x 5 operator Color space converter
Mathematical Operators	CORDIC-based rectangular-to-polar coordinate converter CORDIC-based divider circuit CORDIC-based sine and cosine function Control Logic Debugging a PicoBlaze™ microcontroller design

Audio DSP Design Kit
The Audio DSP Design Kit is similar to the Video DSP Kit, but is optimized for audio processing applications. The kit features a Spartan-IIE hardware board with an XC2S200E-6FT256 FPGA, a TI TLV320AIC23 16-bit audio CODEC, RS-232 port, LEDs and switches, and several expansion connectors.

Customize Your Platform
If the Audio and Video DSP Design Kits are not quite what you need for your design, you can add more hardware, firmware, or software to create a custom platform. Avnet has a variety of hardware add-in modules that can serve as extensions to the basic platform.

Audio/Video Add-in Module
The Audio/Video Module provides additional functionality for DSP applications targeting audio and video processing applications. It interfaces to a host through a standard AvBus connector and provides multiple video interfaces to accommodate RGB monitors, LCD panels, and standard definition television monitors. The module also captures composite video and includes a CODEC to facilitate audio processing. A PS2 keyboard/mouse interface is included as well as a touchscreen controller.

Key elements of the module are:

• Philips™ SAA7113H video input processor
• Philips UCB1400 stereo 20-bit audio CODEC
• Philips SAA7121H digital video encoder
• Analog Devices ADV7123 140 MHz triple video DAC
• Interface for OmniVision™ OV6630AA CMOS color digital camera
• Interface for Fujitsu™ MB86S02A CMOS color digital camera
• AvBus expansion connector interface for Sharp™ LQ057Q3DC02 color TFT LCD module
• X/Y touchscreen controller
• PS2 keyboard and mouse interfaces

Key elements of the module include:

• 64 MB SDRAM
• 16 MB Flash
• 1 MB SRAM
• IrDA
• 10/100/1,000 Ethernet PHY
• USB 2.0
• PC card interface

You can order any of the kits described in this article from your local Avnet sales office, or obtain additional information from the Avnet DSP Startingline website at www.em.avnet.com/dspstartingline/.

Printable PDF version of this article with graphics.  (9/15/04) 268 KB